Method and device for filtering body fluid

ABSTRACT

Medical devices for filtering fluids flowing through a lumen and a method of forming medical devices. The devices can be used in vascular channels, urinary tracts, biliary ducts and the like, and filter emboli and other debris generated at a treatment site.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of application Ser. No.10/051,565, filed Jan. 18, 2002, now U.S. Pat. No. 6,949,103, which is acontinuation of application Ser. No. 08/748,066, filed Nov. 12, 1996,now U.S. Pat. No. 6,605,102, issued Aug. 12, 2003, which is acontinuation of application Ser. No. 08/272,425, filed Jul. 8, 1994, nowabandoned, the contents of each of which are hereby incorporated hereinby reference.

FIELD OF THE INVENTION

The present invention generally relates to intravascular devices fortreating certain medical conditions and, more particularly, provides amethod of forming intravascular devices and certain novel intravascularocclusion devices. The devices made in accordance with the invention areparticularly well suited for delivery through a catheter or the like toa remote location in a patient's vascular system or in analogous vesselswithin a patient's body.

BACKGROUND OF THE INVENTION

A wide variety of intravascular devices are used in various medicalprocedures. Certain intravascular devices, such as catheters andguidewires, are generally used simply to deliver fluids or other medicaldevices to specific locations within a patient's body, such as aselective site within the vascular system. Other, frequently morecomplex, devices are used in treating specific conditions, such asdevices used in removing vascular occlusions or for treating septaldefects and the like.

In certain circumstances, it may be necessary to occlude a patient'svessel, such as to stop blood flow through an artery to a tumor or otherlesion. Presently, this is commonly accomplished simply by inserting,e.g. Ivalon particles, a trade name for vascular occlusion particles,and short sections of coil springs into a vessel at a desired location.These “embolization agents” will eventually become lodged in the vessel,frequently floating downstream of the site at which they are releasedbefore blocking the vessel. In part due to the inability to preciselyposition the embolization agents, this procedure is often limited in itsutility.

Detachable balloon catheters are also used to block patients' vessels.When using such a catheter, an expandable balloon is carried on a distalend of a catheter. When the catheter is guided to the desired location,the balloon is filled with a fluid until it substantially fills thevessel and becomes lodged therein. Resins which will harden inside theballoon, such as an acrylonitrile, can be employed to permanently fixthe size and shape of the balloon. The balloon can then be detached fromthe end of the catheter and left in place.

Such balloon embolizations are also prone to certain safety problems,though. For example, if the balloon is not filled enough, it will not befirmly fixed in the vessel and may drift downstream within the vessel toanother location, much like the loose embolization agents noted above.In order to avoid this problem, physicians may overfill the balloons; itis not uncommon for balloons to rupture and release the resin into thepatient's bloodstream.

In still other procedures, it may not be necessary to permanentlyocclude a vessel, but it may be necessary to provide a filter or thelike to prevent thrombi from passing a particular location. For example,rotating burrs are used in removing atheroma from the lumen of patients'blood vessels. These burrs can effectively dislodge the atheroma, butthe dislodged material will simply float downstream with the flow ofblood through the vessel unless steps are taken to capture the material.

Some researchers have proposed various traps or filters for capturingthe particulate matter released or created in such procedures. However,such filters generally have not proven to be exceptionally effective inactual use. Such filters tend to be cumbersome to use and accuratedeployment is problematic because if they are not properly seated in thevessel they can drift to a more distal site where they are likely to domore harm than good. In addition, these filters are generally capable ofonly trapping relatively large thrombi and are not effective means forremoving smaller embolic particles from the blood stream.

The problems with temporary filters, which are intended to be used onlyduring a particular procedure then retracted with the thrombi trappedtherein, are more pronounced. Even if the trap does effectively capturethe dislodged material, it has proven to be relatively difficult orcomplex to retract the trap back into the catheter through which it wasdelivered without simply dumping the trapped thrombi back into the bloodstream, defeating the purpose of the temporary filter device. For thisreason, most atherectomy devices and the like tend to aspirate thepatient's blood during the procedure to remove the dislodged materialentrained therein.

Mechanical embolization devices, filters and traps have been proposed inthe past. Even if some of those devices have proven effective, they tendto be rather expensive and time-consuming to manufacture. For example,some intravascular blood filters suggested by others are formed of aplurality of specially-shaped legs which are adapted to fill the vesseland dig into the vessel walls. In making most such filters, the legsmust be individually formed and then painstakingly attached to oneanother, frequently entirely by hand, to assemble the final filter. Notonly does this take significant skilled manpower, and hence increase thecosts of such devices, the fact that each item must be made by handtends to make quality control more difficult. This same difficulty andexpense of manufacturing is not limited to such filters, but isexperienced in many other intravascular devices as well.

Accordingly, it would be desirable to provide a method for formingdevices for deployment in a patient's vessel which is both economicaland yields consistent, reproducible results. It would also beadvantageous to provide a reliable embolization device which is botheasy to deploy and can be accurately placed in a vessel. Furthermore,there is a need in the art for a trap or filter which can be deployedwithin a vessel for capturing thrombi, which trap can be reliablydeployed; if the trap is to be used only temporarily, it should bereadily withdrawn from the patient without simply dumping the trappedthrombi back into the blood stream.

SUMMARY OF THE INVENTION

The present invention provides a method for forming intravasculardevices from a resilient metal fabric and medical devices which can beformed in accordance with this method. In the method of the invention, ametal fabric formed of a plurality of resilient strands is provided,with the wires being formed of a resilient material which can be heattreated to substantially set a desired shape. This fabric is thendeformed to generally conform to a molding surface of a molding elementand the fabric is heat treated in contact with the surface of themolding element at an elevated temperature. The time and temperature ofthe heat treatment is selected to substantially set the fabric in itsdeformed state. After the heat treatment, the fabric is removed fromcontact with the molding element and will substantially retain its shapein the deformed state. The fabric so treated defines an expanded stateof a medical device which can be deployed through a catheter into achannel in a patient's body.

In accordance with the method of the invention, a distal end of acatheter can be positioned in a channel in a patient's body to positionthe distal end of the catheter adjacent a treatment site for treating aphysiological condition. A medical device made in accordance with theprocess outlined above can be collapsed and inserted into the lumen ofthe catheter. The device is urged through the catheter and out thedistal end, whereupon it will tend to return to its expanded stateadjacent the treatment site.

Further embodiments of the present invention also provide specificmedical devices which may be made in accordance with the presentinvention. Such devices of the invention are formed of a metal fabricand have an expanded configuration and a collapsed configuration. Thedevices are collapsed for deployment through a catheter and, uponexiting the distal end of the catheter in a patient's channel, willresiliently substantially return to their expanded configuration. Inaccordance with a first of these embodiments, a generally elongatemedical device has a generally tubular middle portion and a pair ofexpanded diameter portions, with one expanded diameter portionpositioned at either end of the middle portion. In another embodiment,the medical device is generally bell-shaped, having an elongate bodyhaving a tapered first end and a larger second end, the second endpresenting a fabric disc which will be oriented generally perpendicularto an axis of a channel when deployed therein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B each depict a metal fabric suitable for use with theinvention;

FIGS. 2A and 2B are a side view and a perspective view, respectively, ofa molding element and a length of a metal fabric suitable for use informing a medical device in accordance with the invention, the moldbeing in a disassembled state;

FIG. 3A is a perspective view showing the molding element and metalfabric of FIG. 2 in a partially assembled state;

FIG. 3B is a close-up view of the highlighted area of FIG. 3A showingthe compression of the metal fabric in the molding element;

FIG. 4 is a cross-sectional view showing the molding element and metalfabric of FIG. 2 in an assembled state;

FIGS. 5A and 5B are a side view and an end view, respectively, of amedical device in accordance with the invention;

FIGS. 6A-6C are a side view, an end view and a perspective view,respectively, of a medical device in accordance with another embodimentof the invention;

FIG. 7 is a side, cross sectional view of a molding element suitable forforming the medical device shown in FIGS. 6A-6C;

FIG. 8 is a schematic illustration showing the device of FIGS. 6A-6Cdeployed in a channel of a patient's vascular system to occlude a PatentDuctus Arteriosus;

FIGS. 9A and 9B are a side view and an end view, respectively, of amedical device in accordance with yet another embodiment of theinvention;

FIG. 10A is a side view of one molding element suitable for forming theinvention of FIGS. 9A and 9B;

FIG. 10B is a cross-sectional view of another molding element suitablefor forming the invention of FIGS. 9A and 9B;

FIG. 10C is a cross-sectional view of still another molding elementsuitable for forming the invention of FIGS. 9A and 9B;

FIG. 11A is a schematic side view of yet another medical device made inaccordance with the invention showing the device in a collapsed statefor deployment in a patient's vascular system;

FIG. 11B is a schematic side view of the medical device of FIG. 11A inan expanded state for deployment in a patient's vascular system;

FIG. 12A is a schematic side view of an alternative embodiment of theinvention of FIG. 11A showing the device in a collapsed state within acatheter for deployment;

FIG. 12B is a schematic side view of the device of FIG. 12A showing thedevice deployed distally of the catheter;

FIG. 13 is a schematic perspective view showing a medical device inaccordance with yet a further embodiment of the invention collapsedwithin a catheter for deployment in a channel in a patient's body;

FIG. 14 is a schematic side view of the device of FIG. 13 in a partiallydeployed state; and

FIG. 15 is a schematic side view of the device of FIG. 13 in a fullydeployed state.

FIG. 16 is a cross-sectional view of one molding element suitable forforming the invention of FIGS. 11A, 11B, 12A, and 12B.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a reproducible, relatively inexpensivemethod of forming devices for use in channels in patients' bodies, suchas vascular channels, urinary tracts, biliary ducts and the like, aswell as devices which may be made via that method. In forming a medicaldevice via the method of the invention, a metal fabric 10 is provided.The fabric is formed of a plurality of wire strands having apredetermined relative orientation between the strands. FIGS. 1A and 1Billustrate two examples of metal fabrics which are suitable for use inthe method of the invention.

In the fabric of FIG. 1A, the metal strands define two sets ofessentially parallel generally helical strands, with the strands of oneset having a “hand”, i.e. a direction of rotation, opposite that of theother set. This defines a generally tubular fabric, known in the fabricindustry as a tubular braid. Such tubular braids are well known in thefabric arts and find some applications in the medical device field astubular fabrics, such as in reinforcing the wall of a guiding catheter.As such braids are well known, they need not be discussed at lengthhere.

The pitch of the wire strands (i.e. the angle defined between the turnsof the wire and the axis of the braid) and the pick of the fabric (i.e.the number of turns per unit length) may be adjusted as desired for aparticular application. For example, if the medical device to be formedis to be used to occlude the channel in which it is placed, the pitchand pick of the fabric will tend to be higher than if the device issimply intended to filter bodily fluid passing therethrough.

For example, in using a tubular braid such as that shown in FIG. 1A toform a device such as that illustrated in FIGS. 5A and 5B, a tubularbraid of about 4 mm in diameter with a pitch of about 50° and a pick ofabout 74 (per linear inch) would seem suitable for a devices used inoccluding channels on the order of about 2 mm to about 4 mm in innerdiameter, as detailed below in connection with the embodiment of FIGS.5A and 5B.

FIG. 1B illustrates another type of fabric which is suitable for use inthe method of the invention. This fabric is a more conventional fabricand may take the form of a flat woven sheet, knitted sheet or the like.In the woven fabric shown in FIG. 1B, there are also two sets 14 and 14′of generally parallel strands, with one set of strands being oriented atan angle, e.g. generally perpendicular (having a pick of about 90°),with respect to the other set. As noted above, the pitch and pick ofthis fabric (or, in the case of a knit fabric, the pick and the patternof the kit, e.g. Jersey or double knits) may be selected to optimize thedesired properties of the final medical device.

The wire strands of the metal fabric used in the present method shouldbe formed of a material which is both resilient and can be heat treatedto substantially set a desired shape. Materials which are believed to besuitable for this purpose include a cobalt-based low thermal expansionalloy referred to in the field as Elgiloy, nickel-based high-temperaturehigh-strength “superalloys” commercially available from HaynesInternational under the trade name Hastelloy, nickel-based heattreatable alloys sold under the name Incoloy by International Nickel,and a number of different grades of stainless steel. The importantfactor in choosing a suitable material for the wires is that the wiresretain a suitable amount of the deformation induced by the moldingsurface (as described below) when subjected to a predetermined heattreatment.

One class of materials which meet these qualifications are so-calledshape memory alloys. Such alloys tend to have a temperature inducedphase change which will cause the material to have a preferredconfiguration which can be fixed by heating the material above a certaintransition temperature to induce a change in the phase of the material.When the alloy is cooled back down, the alloy will “remember” the shapeit was in during the heat treatment and will tend to assume thatconfiguration unless constrained from so doing.

One particularly preferred shape memory alloy for use in the presentmethod is nitinol, an approximately stoichiometric alloy of nickel andtitanium, which may also include other minor amounts of other metals toachieve desired properties. NiTi alloys such as nitinol, includingappropriate compositions and handling requirements, are well known inthe art and such alloys need not be discussed in detail here. Forexample, U.S. Pat. Nos. 5,067,489 (Lind) and 4,991,602 (Amplatz et al.),the teachings of which are incorporated herein by reference, discuss theuse of shape memory NiTi alloys in guidewires. Such NiTi alloys arepreferred, at least in part, because they are commercially available andmore is known about handling such alloys than other known shape memoryalloys. NiTi alloys are also very elastic—they are said to be“superelastic” or “pseudoelastic”. This elasticity will help a device ofthe invention return to a present expanded configuration for deployment.

The wire strands can comprise a standard monofilament of the selectedmaterial, i.e. a standard wire stock may be used. If so desired, though,the individual wire strands may be formed from “cables” made up of aplurality of individual wires. For example, cables formed of metal wireswhere several wires are helically wrapped about a central wire arecommercially available and NiTi cables having an outer diameter of 0.003inches or less can be purchased. One advantage of certain cables is thatthey tend to be “softer” than monofilament wires having the samediameter and formed of the same material. Additionally, if the devicebeing formed from the wire strands is to be used to occlude a vessel,the use of a cable can increase the effective surface area of the wirestrand, which will tend to promote thrombosis.

In preparation of forming a medical device in keeping with theinvention, an appropriately sized piece of the metal fabric is cut fromthe larger piece of fabric which is formed, for example, by braidingwire strands to form a long tubular braid. The dimensions of the pieceof fabric to be cut will depend, in large part, upon the size and shapeof the medical device to be formed therefrom.

When cutting the fabric to the desired dimensions, care should be takento ensure that the fabric will not unravel. In the case of tubularbraids formed of NiTi alloys, for example, the individual wire strandswill tend to return to their heat-set configuration unless constrained.If the braid is heat treated to set the strands in the braidedconfiguration, they will tend to remain in the braided form and only theends will become frayed. However, it may be more economical to simplyform the braid without heat treating the braid since the fabric will beheat treated again in forming the medical device, as noted below.

In such untreated NiTi fabrics, the strands will tend to return to theirunbraided configuration and the braid can unravel fairly quickly unlessthe ends of the length of braid cut to form the device are constrainedrelative to one another. One method which has proven to be useful toprevent the braid from unraveling is to clamp the braid at two locationsand cut the braid to leave a length of the braid having clamps (15 inFIG. 2) at either end, thereby effectively defining an empty spacewithin a sealed length of fabric. These clamps 15 will hold the ends ofthe cut braid together and prevent the braid from unraveling.

Alternatively, one can solder, braze, weld or otherwise affix the endsof the desired length together (e.g. with a biocompatible cementitiousorganic material) before cutting the braid. Although soldering andbrazing of NiTi alloys has proven to be fairly difficult, the ends canbe welded together, such as by spot welding with a laser welder.

The same problems present themselves when a flat sheet of fabric such asthe woven fabric shown in FIG. 1B is used. With such a fabric, thefabric can be inverted upon itself to form a recess or depression andthe fabric can be clamped about this recess to form an empty pocket (notshown) before the fabric is cut. If it is desired to keep the fabric ina generally flat configuration, it may be necessary to weld thejunctions of the strands together adjacent the periphery of the desiredpiece of fabric before that piece is cut from the larger sheet. Soconnecting the ends of the strands together will prevent fabrics formedof untreated shape memory alloys and the like from unraveling during theforming process.

Once an appropriately sized piece of the metal fabric is obtained, thefabric is deformed to generally conform to a surface of a moldingelement. As will be appreciated more fully from the discussion below inconnection with FIGS. 2-16, so deforming the fabric will reorient therelative positions of the strands of the metal fabric from their initialorder to a second, reoriented configuration. The shape of the moldingelement should be selected to deform the fabric into substantially theshape of the desired medical device.

The molding element can be a single piece, or it can be formed of aseries of mold pieces which together define the surface to which thefabric will generally conform. The molding element can be positionedwithin a space enclosed by the fabric or can be external of such aspace, or can even be both inside and outside such a space.

In order to illustrate one example of how such a mold may be configuredand how it may be used in accordance with the method of the invention,reference will be had to FIGS. 2-5. In FIGS. 2-4, the molding element 20is formed of a number of separate pieces which can be attached to oneanother to complete the molding element 20. In using such a multi-piecemolding element, the mold can be assembled about the cut length offabric 10, thereby deforming the fabric to generally conform to thedesired surface (or surfaces) of the molding element.

In the molding element illustrated in FIGS. 2-4, the metal fabric 10 isdeformed to generally conform to a surface of the molding element 20,the molding element comprising a center section 30 and a pair of endplates 40. Turning first to the center section 30, the center section isdesirably formed of opposed halves 32, 32 which can be moved away fromone another in order to introduce the metal fabric 10 into the mold.Although these two halves 32, 32 are shown in the drawings as beingcompletely separated from one another, it is to be understood that thesehalves could be interconnected, such as by means of a hinge or the like,if so desired. The opposed halves of the molding element 20 shown in thedrawings of FIGS. 2 and 3 each include a pair of semi-circular recessesopposed on either side of a ridge defining a generally semi-circularopening. When the two halves are assembled in forming the device, asbest seen in FIG. 3, the semi-circular openings in the opposed halves32, 32 mate to define a generally circular forming port 36 passingthrough the center section 30. Similarly, the semi-circular recesses inthe two halves together form a pair of generally circular centralrecesses 34, with one such recess being disposed on either face of thecenter section.

The overall shape and dimensions of the center section can be varied asdesired; it is generally the size of the central recesses 34 and theforming port 36 which will define the size and shape of the middle ofthe finished device, as explained below. If so desired, each half 32 maybe provided with a manually graspable projection 38. In the embodimentshown in the drawings, this projection 38 is provided at a locationdisposed away from the abutting faces of the respective halves. Such amanually graspable projection 38 will simply enable an operator to moreeasily join the two halves to define the recesses 34 and forming port36.

The center section is adapted to cooperatively engage a pair of endplates 40 for forming the desired device. In the embodiment shown inFIGS. 2 and 3, the center section 30 has a pair of flat outer faces 39which are each adapted to be engaged by an inner face 42 of one of thetwo end plates 40. Each end plate includes a compression disk 44 whichextends generally laterally inwardly from the inner face 42 of the endplate. This compression disk 44 should be sized to permit it to bereceived within one of the central recesses 34 on either face of thecenter section 30. For reasons explained more fully below, eachcompression disk 44 includes a cavity 46 for receiving an end of thelength of the metal fabric 10.

One or more channels 48 for receiving bolts and the like may also beprovided through each of the end plates and through the center section30. By passing bolts through these channels 48, one can assemble themolding element 20 and retain the metal fabric in the desired shapeduring the heat treatment process, as outlined below.

In utilizing the molding element 20 shown in FIGS. 2-4, a length of themetal fabric 10 can be positioned between the opposed halves 32 of thecenter section 30. In the drawings of the molding element 20 of FIGS.2-4, the metal fabric 10 is a tubular braid such as that illustrated inFIG. 1A. A sufficient length of the tubular braid should be provided topermit the fabric to conform to the molding surface, as explained below.Also, as noted above, care should be taken to secure the ends of thewire strands defining the tubular braid in order to prevent the metalfabric from unraveling.

A central portion of the length of the metal braid may be positionedwithin one of the two halves of the forming port 36 and the opposedhalves 32 of the center section may be joined to abut one another torestrain a central portion of the metal braid within the central formingport 36 through the center section.

The tubular braid will tend to have a natural, relaxed diameter which isdefined, in large part, when the tubular braid is formed. Unless thetubular braid is otherwise deformed, when the wire strands are in theirrelaxed state they win tend to define a generally hollow tube having thepredetermined diameter. The outer diameter of the relaxed braid may be,for example, about 4 mm. The relative size of the forming port 36 in thecentral section 30 of the molding element and the natural, relaxed outerdiameter of the tubular braid may be varied as desired to achieve thedesired shape of the medical device being formed.

In the embodiment shown in FIGS. 2 and 3, the inner diameter of theforming port 36 is optimally slightly less than the natural, relaxedouter diameter of the tubular braid 10. Hence, when the two halves 32,32 are assembled to form the center section 30, the tubular braid 10will be slightly compressed within the forming port 36. This will helpensure that the tubular braid conforms to the inner surface of theforming port 36, which defines a portion of the molding surface of themolding element 20.

If so desired, a generally cylindrical internal molding section (notshown) may also be provided. This internal molding section has aslightly smaller diameter than the inner diameter of the forming port36. In use, the internal molding section is placed within the length ofthe metal fabric, such as by manually moving the wire strands of thefabric apart to form an opening through which the internal moldingsection can be passed. This internal molding section should bepositioned within the tubular braid at a location where it will bedisposed within the forming port 36 of the center section when themolding element is assembled. There should be a sufficient space betweenthe outer surface of the interior molding section and the inner surfaceof the forming port 36 to permit the wire strands of the fabric 10 to bereceived therebetween.

By using such an internal molding section, the dimensions of the centralportion of the finished medical device can be fairly accuratelycontrolled. Such an internal molding section may be necessary incircumstances where the natural, relaxed outer diameter of the tubularbraid 10 is less than the inner diameter of the forming port 36 toensure that the braid conforms to the inner surface of that formingport. However, it is not believed that such an internal molding sectionwould be necessary if the natural, relaxed outer diameter of the braidwere larger than the inner diameter of the forming port 36.

As noted above, the ends of the tubular braid should be secured in orderto prevent the braid from unraveling. Each end of the metal fabric 10 isdesirably received within a cavity 46 formed in one of the two endplates 40. If a clamp (15 in FIG. 2) is used, the clamp may be sized tobe relatively snugly received within one of these cavities 46 in orderto effectively attach the end of the fabric to the end plate 40. The endplates can then be urged toward the center section 30 and toward oneanother until the compression disk 44 of each end plate is receivedwithin a central recess 34 of the center section 30. The molding elementmay then be clamped in position by passing bolts or the like through thechannels 48 in the molding element and locking the various components ofthe molding element together by tightening a nut down onto such a bolt(not shown).

As best seen in FIG. 3A, when an end plate is urged toward the centersection 30, this will compress the tubular braid 10 generally along itsaxis. When the tubular braid is in its relaxed configuration, asillustrated in FIG. 1A, the wire strands forming the tubular braid willhave a first, predetermined relative orientation with respect to oneanother. As the tubular braid is compressed along its axis, the fabricwill tend to flare out away from the axis, as illustrated in FIG. 4.When the fabric is so deformed, the relative orientation of the wirestrands of the metal fabric will change. When the molding element isfinally assembled, the metal fabric will generally conform to themolding surface of this element.

In the molding element 20 shown in FIGS. 2-4, the molding surface isdefined by the inner surface of the forming port, the inner surfaces ofthe central recess 34 and the faces of the compression disks 44 whichare received within the recesses 34. If an internal molding section isused, the cylindrical outer surface of that section may also beconsidered a part of the molding surface of the molding element 20.Accordingly, when the molding element 20 is completely assembled themetal fabric will tend to assume a somewhat “dumbbell”-shapedconfiguration, with a relatively narrow center section disposed betweena pair of bulbous, perhaps even disk-shaped end sections, as best seenin FIG. 4.

It should be understood that the specific shape of the particularmolding element 20 shown in FIGS. 2-4 is intended to produce one usefulmedical device in accordance with the present method, but that othermolding elements having different configurations could also be used. Ifa more complex shape is desired, the molding element may have moreparts, but if a simpler shape is being formed the molding element mayhave even fewer parts. The number of parts in a given molding elementand the shapes of those parts will be dictated almost entirely by theshape of the desired medical device as the molding element must define amolding surface to which the metal fabric will generally conform.

Accordingly, the specific molding element 20 shown in FIGS. 2-4 issimply intended as one specific example of a suitable molding elementfor forming one particular useful medical device. Additional moldingelements having different designs for producing different medicaldevices are explained below in connection with, e.g., FIGS. 8 and 10.Depending on the desired shape of the medical device being formed, theshape and configuration of other specific molding elements can bereadily designed by those of ordinary skill in the art.

Once the molding element 20 is assembled with the metal fabric generallyconforming to a molding surface of that element, the fabric can besubjected to a heat treatment while it remains in contact with thatmolding surface. This heat treatment will depend in large part upon thematerial of which the wire strands of the metal fabric are formed, butthe time and temperature of the heat treatment should be selected tosubstantially set the fabric in its deformed state, i.e., wherein thewire strands are in their reoriented relative configuration and thefabric generally conforms to the molding surface.

The time and temperature of the heat treatment can vary greatlydepending upon the material used in forming the wire strands. As notedabove, one preferred class of materials for forming the wire stands areshape memory alloys, with nitinol, a nickel titanium alloy, beingparticularly preferred. If nitinol is used in making the wire strands ofthe fabric, the wire strands will tend to be very elastic when the metalis in its austenitic phase; this very elastic phase is frequentlyreferred to as a “superelastic” or “pseudoelastic” phase. By heating thenitinol above a certain phase transition temperature, the crystalstructure of the nitinol metal when in its austenitic phase can be set.This will tend to “set” the shape of the fabric and the relativeconfiguration of the wire strands in the positions in which they areheld during the heat treatment.

Suitable heat treatments of nitinol wire to set a desired shape are wellknown in the art. Spirally wound nitinol coils, for example, are used ina number of medical applications, such as in forming the coils commonlycarried around distal lengths of guidewires. A wide body of knowledgeexists for forming nitinol in such medical devices, so there is no needto go into great detail here on the parameters of a heat treatment forthe nitinol fabric preferred for use in the present invention.

Briefly, though, it has been found that holding a nitinol fabric atabout 500° C. to about 550° C. for a period of about 1 to about 30minutes, depending on the softness or harness of the device to be made,will tend to set the fabric in its deformed state, i.e. wherein itconforms to the molding surface of the molding element. At lowertemperatures the heat treatment time will tend to be greater (e.g. aboutone hour at about 350° C.) and at higher temperatures the time will tendto be shorter (e.g. about 30 seconds at about 900° C.). These parameterscan be varied as necessary to accommodate variations in the exactcomposition of the nitinol, prior heat treatment of the nitinol, thedesired properties of the nitinol in the finished article, and otherfactors which will be well known to those skilled in this field.

Instead of relying on convection heating or the like, it is also knownin the art to apply an electrical current to the nitinol to heat it. Inthe present invention, this can be accomplished by, for example, hookingelectrodes to the clamps 15 carried at either end of the metal fabricillustrated in FIG. 2. The wire can then be heated by resistance heatingof the wires in order to achieve the desired heat treatment, which willtend to eliminate the need to heat the entire molding element to thedesired heat treating temperature in order to heat the metal fabric tothe desired temperature.

After the heat treatment, the fabric is removed from contact with themolding element and will substantially retain its shape in a deformedstate. When the molding element 20 illustrated in FIGS. 2-4 is used, thebolts (not shown) may be removed and the various parts of the moldingelement may be disassembled in essentially the reverse of the process ofassembling the molding element. If an internal molding section is used,this molding section can be removed in much the same fashion that it isplaced within the generally tubular metal fabric in assembling themolding element 20, as detailed above.

FIGS. 5A and 5B illustrate one embodiment of a medical device 60 whichmay be made using the molding element 20 of FIGS. 2-4. As discussedbelow, the device of FIG. 5 is particularly well suited for use inoccluding a channel within a patient's body and these designs haveparticular advantages in use as vascular occlusion devices.

The vascular occlusion device 60 of FIG. 5A includes a generally tubularmiddle portion 62 and a pair of expanded diameter portions 64. Oneexpanded diameter portion is disposed at either end of the generallytubular middle portion 62. In the embodiment shown in FIGS. 5A and 5B,the expanded diameter portions 64 include a ridge 66 positioned aboutmidway along their lengths.

The relative sizes of the tubular middle section and the expandeddiameter portions can be varied as desired. In this particularembodiment, the medical device is intended to be used as a vascularocclusion device to substantially stop the flow of blood through apatient's blood vessel. When the device 60 is deployed within apatient's blood vessel, as detailed below, it will be positioned withinthe vessel such that its axis generally coincides with the axis of thevessel. The dumbbell-shape of the present device is intended to limitthe ability of the vascular occlusion device 60 to turn at an angle withrespect to the axis of the blood vessel to ensure that it remains insubstantially the same position in which the operator deploys it withinthe vessel.

Although the illustrated embodiments of this invention only have twoexpanded diameter portions, it should be understood that the devicecould have more than two such expanded diameter portions. For example,if the device has three expanded diameter portions, each expandeddiameter portion is separated from at least one other expanded diameterportion by a tubular portion having a smaller diameter. If so desired,the diameters of each of the expanded diameter portions can be the same,but they need not be the same.

In order to relatively strongly engage the lumen of the blood vessel,the maximum diameter of the expanded diameter portions 64 (which occursalong the middle ridge 66 in this embodiment) should be selected so thatit is at least as great as the diameter of the lumen of the vessel inwhich it is to be deployed, and is optimally slightly greater than thatdiameter. When it is deployed within the patient's vessel, the vascularocclusion device 60 will engage the lumen at two spaced-apart locations.The device 60 is desirably longer along its axis than the dimension ofits greatest diameter. This will substantially prevent the vascularocclusion device 60 from turning within the lumen at an angle to itsaxis, essentially preventing the device from becoming dislodged andtumbling along the vessel with blood flowing through the vessel.

The relative sizes of the generally tubular middle portion 62 andexpanded diameter portion 64 of the vascular occlusion device 60 can bevaried as desired for any particular application. For example, the outerdiameter of the middle portion 62 may range between about one quarterand about one third of the maximum diameter of the expanded diameterportions 64 and the length of the middle portion 62 may comprise about20% to about 50% of the overall length of the device. Although thesedimensions are suitable if the device 60 is to be used solely foroccluding a vascular vessel, it is to be understood that thesedimensions may be varied if the device is to be used in otherapplications, such as where the device is intended to be used simply asa vascular filter rather than to substantially occlude the entire vesselor where the device is deployed in a different channel in a patient'sbody.

The aspect ratio (i.e., the ratio of the length of the device over itsmaximum diameter or width) of the device 60 illustrated in FIGS. 5A and5B is desirably at least about 1.0, with a range of about 1.0 to about3.0 being preferred and an aspect ratio of about 2.0 being particularlypreferred. Having a greater aspect ration will tend to prevent thedevice from rotating generally perpendicularly to its axis, which may bereferred to as an end over end roll. So long as the outer diameter ofthe expanded diameter portions 64 of the device is large enough to seatthe device fairly securely against the lumen of the channel in which thedevice is deployed, the inability of the device to turn end over endwill help keep the device deployed precisely where it is positionedwithin the patient's vascular system or in any other channel in thepatient's body. Alternatively, having expanded diameter portions whichhave natural, relaxed diameters substantially larger than the lumen ofthe vessels in which the device is deployed should also suffice to wedgethe device into place in the vessel without undue concern being placedon the aspect ratio of the device.

The pick and pitch of the metal fabric 10 used in forming the device 60,as well as some other factors such as the number of wires employed in atubular braid, are important in determining a number of the propertiesof the device. For example, the greater the pick and pitch of thefabric, and hence the greater the density of the wire strands in thefabric, the stiffer the device will be. Having a greater wire densitywill also provide the device with a greater wire surface area, whichwill generally enhance the tendency of the device to occlude a bloodvessel in which it is deployed. This thrombogenicity can be eitherenhanced, e.g. by a coating of a thrombolytic agent or by attaching silkor wool fabric to the device, or abated, e.g. by a coating of alubricious, anti-thrombogenic compound. A variety of materials andtechniques for enhancing or reducing thrombogenicity are well known inthe art and need not be detailed here.

When the device is deployed in a patient's vessel, thrombi will tend tocollect on the surface of the wires. By having a greater wire density,the total surface area of the wires will be increased, increasing thethrombolytic activity of the device and permitting it to relativelyrapidly occlude the vessel in which it is deployed. It is believed thatforming the occlusion device 60 from a 4 mm diameter tubular braidhaving a pick of at least about 40 and a pitch of at least about 30°will provide sufficient surface area to substantially completely occludea blood vessel of 2 mm to about 4 mm in inner diameter in a suitableperiod of time. If it is desired to increase the rate at which thedevice 60 occludes the vessel in which it is deployed, any of a widevariety of known thrombolytic agents can be applied to the device.

FIGS. 6A-6C illustrate an alternative embodiment of a medical device inaccordance with the present invention. This device 80 has a generallybell-shaped body 82 and an outwardly extending forward end 84. Oneapplication for which this device is particularly well suited isoccluding defects known in the art as patent ductus arteriosus (PDA).PDA is essentially a condition wherein two blood vessels, most commonlythe aorta and pulmonary artery adjacent the heart, have a shunt betweentheir lumens. Blood can flow directly between these two blood vesselsthrough the shunt, compromising the normal flow of blood through thepatient's vessels.

As explained more fully below in connection with FIG. 8, the bell-shapedbody 82 is adapted to be deployed within the shunt between the vessels,while the forward end 84 is adapted to be positioned within one of thetwo vessels to help seat the body in the shunt. The sizes of the body 82and the end 84 can be varied as desired for differently sized shunts.For example, the body may have a diameter along its generallycylindrical middle 86 of about 10 mm and a length along its axis ofabout 25 mm. In such a device, the base 88 of the body may flaregenerally radially outward until it reaches an outer diameter equal tothat of the forward end 84, which may be on the order of about 20 mm indiameter.

The base 88 desirably flares out relatively rapidly to define a shouldertapering radially outwardly from the middle 86 of the body. When thedevice is deployed in a vessel, this shoulder will abut the lumen of oneof the vessels being treated. The forward end 84 is retained within thevessel and urges the base 88 of the body open to ensure that theshoulder engages the wall of the vessel to prevent the device 80 frombecoming dislodged from within the shunt.

As detailed above, in making a device of the invention it is desirableto attach the ends of the wire strands forming the metal fabric 10 toone another to prevent the fabric from unraveling. In the illustrationsof FIGS. 6A-6C, a clamp 15 is used to tie together the ends of the wirestrands adjacent the front end 84 of the device. It is to be understoodthat this clamp 15 is simply a schematic illustration, though, and thatthe ends could be attached in other ways, such as by welding, soldering,brazing, use of a biocompatible cementitious material or in any othersuitable fashion.

The rearward ends of the wire strands are shown as being attached to oneanother by an alternative clamping means 90. This clamp 90 serves thesame purpose as the schematically illustrated clamp 15, namely tointerconnect the ends of the wires. However the clamp 90 also serves toconnect the device 80 to a delivery system (not shown). In theembodiment shown, the clamp 90 is generally cylindrical in shape and hasa recess for receiving the ends of the wires to substantially preventthe wires from moving relative to one another, and a threaded outersurface. The threaded outer surface is adapted to be received within acylindrical recess (not shown) on a distal end of a delivery device andto engage the threaded inner surface of the delivery device's recess.

The delivery device (not shown) can take any suitable shape, butdesirably comprises an elongate, flexible metal shaft having such arecess at its distal end. The delivery device can be used to urge thePDA occlusion device 80 through the lumen of a catheter for deploymentin a channel of the patient's body, as outlined below. When the deviceis deployed out the distal end of the catheter, the device will still beretained by the delivery device. Once the proper position of the device80 in the shunt is confirmed, the shaft of the delivery device can berotated about its axis to unscrew the clamp 90 from the recess in thedelivery means.

By keeping the PDA device 80 attached to the delivery means, theoperator could still retract the device for repositioning if it isdetermined that the device is not properly positioned in the firstattempt. This threaded attachment will also allow the operator tocontrol the manner in which the device 80 is deployed out of the distalend of the catheter. As explained below, when the device exits thecatheter it will tend to resiliently return to a preferred expandedshape which is set when the fabric is heat treated. When the devicesprings back into this shape, it may tend to act against the distal endof the catheter, effectively urging itself forward beyond the end of thecatheter. This spring action could conceivably result in improperpositioning of the device if the location of the device within a channelis critical, such as where it is being positioned in a shunt between twovessels. Since the threaded clamp 90 can enable the operator to maintaina hold on the device during deployment, the spring action of the devicecan be controlled and the operator can control the deployment to ensureproper positioning.

A PDA occlusion device 80 of this embodiment of the invention canadvantageously be made in accordance with the method outlined above,namely deforming a metal fabric to generally conform to a moldingsurface of a molding element and heat treating the fabric tosubstantially set the fabric in its deformed state. FIG. 7 shows amolding element 100 which may be suitable for forming a PDA occlusiondevice 80 such as that shown in FIGS. 6A-6C.

The molding element 100 generally comprises a body portion 110 and anend plate 120. The body portion 110 is adapted to receive and form thebody 82 of the device 80 while the end plate is adapted to compressagainst the metal fabric to form the forward end 84. The body portion110 includes an elongate, generally tubular central segment 112 which issized to receive the elongate body 82 of the device. The central segment112 of the molding element 100 optimally has an internal diameterslightly less than the natural, relaxed outer diameter of the tubularbraid of which the device is formed. This compression of the braid willhelp yield devices with reproducibly sized bodies 82. The forward end ofthe body portion 110 includes a back plate 114 which has a generallyannular sidewall 116 depending downwardly therefrom. The sidewalldefines a recess 118 which is generally circular in shape.

The end plate 120 of the molding element 100 has a generally disc-shapedface 122, which desirably has a clamp port 124 approximately centeredtherein for receiving a clamp 15 attached to the metal fabric, as notedabove. The end plate also has an annular sidewall 126 which extendsgenerally upwardly from the face 122 to define a generally cylindricalrecess 128 in the end plate 120. The sidewall 116 of the body portion110 is sized to be received within the recess 128 of the end plate.

In use, the metal fabric is placed in the molding element and the bodyportion 110 and the end plate 120 are brought toward one another. Theinner face of the back plate 114 will engage the fabric and tend to urgeit under compression generally radially outwardly. The fabric will thenbe enclosed generally within the recess 118 of the body portion and willgenerally conform to the inner surface of that recess. If one preventsthe entire clamp 15 from passing through the clamp port 124, the fabricwill be spaced slightly away from the inner surface of the face 122,yielding a slight dome shape in the forward end 84 of the device, asillustrated in FIGS. 6. Although the illustrated embodiment includessuch a dome-shaped forward end, it is to be understood that the forwardend may be substantially flat (except for the clamp 15), which can beaccomplished by allowing the clamp to be received entirely within theclamp port 124 in the end plate.

Once the fabric is compressed in the molding element 100 so that itgenerally conforms to the molding surface of the molding element, thefabric can be subjected to a heat treatment such as is outlined above.When the molding element is opened again by moving the body portion 110and the end plate 120 away from one another again, the fabric willgenerally retain its deformed, compressed configuration. The device canthen be collapsed, such as by urging the clamps 15, 90 generally axiallyaway from one another, which will tend to collapse the device toward itsaxis. The collapsed device 80 can then be passed through a catheter fordeployment in a channel in a patient's vascular system.

FIG. 8 schematically illustrates how a medical device 80 generally asoutlined above can be used to occlude a patent ductus arteriosus. Inthis case, there is a shunt, referred to as a PDA above, which extendsbetween a patient's aorta A and the pulmonary artery P. The device 80can be passed through the PDA, such as by keeping the device collapsedwithin a catheter (not shown), and the forward end 84 of the device canbe allowed to elastically expand to substantially recover its thermallyset, “remembered” shape from the heat treatment process, such as byurging the device distally to extend beyond the distal end of thecatheter. This forward end 84 should be larger than the lumen of theshunt of the PDA.

The device can then be retracted so that the forward end 84 engages thewall of the pulmonary artery P. If one continues to retract thecatheter, the engagement of the device with the wall of the pulmonaryartery will tend to naturally pull the body portion 82 of the devicefrom the catheter, which will permit the body portion to return to itsexpanded configuration. The body portion should be sized so that it willfrictionally engage the lumen of the PDA's shunt. The device 80 willthen be held in place by the combination of the friction between thebody portion and the lumen of the shunt and the engagement between thewall of the pulmonary artery and the forward end 84 of the device. Overa relatively short period of time, thrombi will form in and on thedevice 80 and the thrombi will occlude the PDA. If so desired, thedevice may be coated with a suitable thrombolytic agent to speed up theocclusion of the PDA.

FIGS. 9A and 9B are a side view and an end view, respectively, of yetanother embodiment of the present invention. This device 180 can be usedfor a variety of applications in a patient's blood vessels. For example,if a fabric having a relatively high pick (i.e. where the wire densityis fairly great) is used in making the device, the device can be used toocclude blood vessels. In other applications, it may serve as a filterwithin a channel of a patient's body, either in a blood vessel or inanother channel, such as in a urinary tract or biliary duct. In order tofurther enhance or reduce the device's tendency to occlude the vessel,depending on the application of the device a suitable known thrombogenicor antithrombogenic coating may be applied to the device.

This filter 180 has a generally conical configuration, taperinggenerally radially outwardly from its rearward end 182 to its forwardend 184. A length of the device adjacent its forward end is adapted toengage the walls of a lumen of a channel. The maximum diameter of thefilter device 180 is therefore at least as large as the inner diameterof the channel in which it is to be positioned so that at least theforward end will engage the wall of the vessel to substantially lock thedevice in place.

Having a series of unsecured ends 185 of the wire strands adjacent theforward end of the device will assist in seating the device in thechannel because the ends of the wires will tend to dig into the vesselwall slightly as the forward end of the device urges itself toward itsfullyexpanded configuration within the vessel. The combination of thefriction between the outwardly urging forward end of the device and thetendency of the wire ends to dig into the vessel walls will help ensurethat the device remains in place where it is deployed rather thanfloating freely within a vessel to reach an undesired location.

The method in which the device 180 of the invention is deployed may varydepending on the nature of the physiological condition to be treated.For example, in treating an arterio-venous fistula, the device may becarefully positioned, as described above, to occlude the flow of bloodat a fairly specific location. In treating other conditions (e.g. anarterio-venous malformation), however, it may be desired to simplyrelease a number of these devices upstream of the malformation in avessel having a larger lumen and simply allow the devices to drift fromthe treatment site to lodge in smaller vessels downstream.

The decision as to whether the device 180 should be precisely positionedat an exact location within the channel in a patient's body or whetherit is more desirable to allow the device(s) to float to their finallodging site will depend on the size of the channels involved and thespecific condition to be treated. This decision should be left to theindividual operator to be made on a case-by-case basis as his or herexperience dictates; there is no one right or wrong way to deploy thedevice 180 without regard to the conditions at hand.

In the embodiment shown in FIGS. 9A and 9B, the wall of the deviceextends generally linearly from a position adjacent the clamp 90 and theother end of the device, approximating a conical shape. Due to thepresence of the clamp 90, though, the end of the device immediatelyadjacent the clamp may deviate slightly from the cone shape, asindicated in the drawings. Alternatively, the wall may be curved so thatthe diameter of the device changes more rapidly adjacent the rearwardend than it does adjacent its forward end, having an appearance morelike a rotation of a parabola about its major axis than a true cone.Either of these embodiments should suffice in occluding a vessel withthe device 180, such as to occlude a vessel.

The ends of the wire strands at the rearward end 182 of the device aresecured with respect to one another, such as by means of a threadedclamp 90 such as that described above in connection with FIGS. 6A-AC.Portions of the wire strands adjacent the forward end 184 may also besecured against relative movement, such as by spot welding wires to oneanother where they cross adjacent the forward end. Such a spot weld isschematically illustrated at 186 in FIGS. 9A and 9B.

In the embodiment illustrated in FIGS. 9, though, the ends of the wirestrands adjacent the forward end 184 in the finished device need not beaffixed to one another in any fashion. These strands are held in a fixedposition during the forming process to prevent the metal fabric fromunraveling before it is made into a finished device. While the ends ofthe wire strands adjacent the forward end remain fixed relative to oneanother, they can be heat treated, as outlined above. The heat treatmentwill tend to fix the shapes of the wires in their deformed configurationwherein the device generally conforms to a molding surface of themolding element. When the device is removed from contact with themolding element, the wires will retain their shape and tend to remainintertwined. Accordingly, when the device is released from contact withthe molding element, even if the ends of the wires are released from anyconstraint the device should still substantially retain its shape.

FIGS. 10A-10C illustrate three suitable molds for use in forming thefilter 180 of FIGS. 9A and 9B. In FIG. 10A, the molding element 200 is asingle piece which defines a pair of generally conical portions abuttingone another. In another similar embodiment (not shown), the moldingelement 200 may be generally ovoid, shaped not unlike an Americanfootball or a rugby ball. In the embodiment illustrated in FIG. 10A,though, the molding element is a little bit less rounded. This moldingelement comprises two conical segments 202 which abut one another attheir bases, defining a larger diameter at the middle 204 of the elementwhich can taper relatively uniformly toward the ends 206 of the element200.

When a tubular braid is used in forming this device, the tubular metalfabric may be applied to the molding element by placing the moldingelement within the tubular braid and clamping the ends of the braidabout the molding element before cutting the braid to the desiredlength. In order to better facilitate the attachment of the clamps 90 tothe ends of the tubular braid, the ends 206 of the molding element maybe rounded, as shown, rather than tapering to a sharper point at theends of the molding element. In order to ensure that the braid moreclosely conforms to the outer surface of the molding element 200, i.e.the molding element's molding surface, the natural, relaxed diameter ofthe braid should be less than the maximum diameter of the element, whichoccurs at its middle 204. This will place the metal fabric in tensionabout the middle of the element and, in combination with the clamps atthe ends of the braid, cause the braid to generally conform to themolding surface.

FIG. 10B illustrates an alternative molding element 210 for forming adevice substantially as shown in FIGS. 9A and 9B. Whereas the moldingelement 200 is intended to be received within a recess in the metalfabric, such as within the lumen of a length of tubular braid, themolding element 210 has an internal cavity 212 adapted to receive thefabric. In this embodiment, the molding element may comprise a pair ofmolding sections 214, 216 and these mold sections may be substantiallyidentical in shape. Each of the molding sections 214, 216 generallycomprise a conical inner surface 220 defined by a wall 222. Each sectionalso may be provided with a generally cylindrical axial recess 224 forreceiving a clamp 15 (or 90) carried by an end of the metal fabric.

The two molding sections should be readily attached to one another withthe larger, open ends 226 of the sections abutting one another. The moldsections can simply be clamped together, such as by providing a reusablejig (not shown) which can be used to properly position the sections 214,216 with respect to one another. If so desired, bolt holes 228 or thelike may be provided to allow a nut and bolt, or any similar attachmentsystem, to be passed through the holes and attach the sections 214, 216together.

In use, a suitably sized piece of a metal fabric, optimally a length ofa tubular braid, is placed in the recess 212 of the molding element andthe two molding sections 214, 216 are urged toward one another. Thefabric should have a relaxed axial length longer than the axial lengthof the recess 212 so that bringing the sections toward one another willaxially compress the fabric. This axial compression will tend to urgethe wire strands of the braid radially outwardly away from the axis ofthe braid and toward engagement with the molding surface of the element210, which is defined by the surface of the recess 212.

Once the metal fabric is deformed to generally conform to the moldingsurface of either molding element 200 or 210, the fabric can be heattreated to substantially set the shape of the fabric in its deformedstate. If molding element 200 is used, it can then be removed from theinterior of the metal fabric. If there is sufficient room between theresilient wire strands, the molding element can simply be removed byopening the web of wire strands and pulling the molding element out ofthe interior of the metal fabric. If molding element 210 is employed,the two molding sections 214, 216 can be moved away from one another andthe molded fabric can be retrieved from the recess 212. Depending on theshape of the molding surface, the resulting formed shape may resembleeither a pair of abutting hollow cones or, as noted above, a football,with clamps, welds or the like provided at either end of the shape.

This shape can then be cut into two halves by cutting the wires in adirection generally perpendicular to the shared axis of the cones (orthe major axis of the ovoid shape) at a location about midway along itslength. This will produce two separate filter devices 180 substantiallyas illustrated in FIGS. 9A and 9B. If the wires strands are to be joinedadjacent the forward end of the device (such as by the weldments shownas 186 in FIGS. 9A and 9B), this can be done before the conical or ovoidshape is severed into two halves. Much the same net shape could beaccomplished by cutting the metal fabric into halves while it is stillcarried about molding element 200. The separate halves having thedesired shape could then be pulled apart from one another, leaving themolding element ready for forming additional devices.

In an alternative embodiment of this method, the molding element 200 isformed of a material selected to permit the molding element to bedestroyed for removal from the interior of the metal fabric. Forexample, the molding element may be formed of a brittle or friablematerial, such as glass. Once the material has been heat treated incontact with the molding surface of the molding element, the moldingelement can be broken into smaller pieces which can be readily removedfrom within the metal fabric. If this material is glass, for example,the molding element and the metal fabric can be struck against a hardsurface, causing the glass to shatter. The glass shards can then beremoved from the enclosure of the metal fabric. The resultant shape canbe used in its generally conical shape, or it can be cut into twoseparate halves to produce a device substantially as shown in FIGS. 9Aand 9B.

Alternatively, the molding element 200 can be formed of a material whichcan be chemically dissolved, or otherwise broken down, by a chemicalagent which will not substantially adversely affect the properties ofthe metal wire strands. For example, the molding element can be formedof a temperature-resistant plastic resin which is capable of beingdissolved with a suitable organic solvent. The fabric and the moldingelement can be subjected to a heat treatment to substantially set theshape of the fabric in conformance with the surface of the moldingelement, whereupon the molding element and the metal fabric can beimmersed in the solvent. Once the molding element is substantiallydissolved, the metal fabric can be removed and either used in itscurrent shape or cut into separate halves, as outlined above.

Care should be taken to ensure that the material selected to form themolding element is capable of withstanding the heat treatment withoutlosing its shape, at least until the shape of the fabric has been set.For example, the molding element could be formed of a material having amelting point above the temperature necessary to set the shape of thewire strands, but below the melting point of the metal forming thestrands. The molding element and metal fabric can then be heat treatedto set the shape of the metal fabric, whereupon the temperature can beincreased to substantially completely melt the molding element, therebyremoving the molding element from within the metal fabric.

It should be understood that the methods outlined immediately above forremoving the metal fabric 10 from the molding element 200 can be used inconnection with other shapes, as well. Although these methods may not benecessary or desirable if the molding element is carried about theexterior of the metal fabric (such as are elements 30-40 of the moldingelement 20 of FIGS. 2-4), if the molding element or some portion thereofis enclosed within the formed metal fabric (such as the internal moldingsection of the molding element 20), these methods can be used toeffectively remove the molding element without adversely affecting themedical device being formed.

FIG. 10C illustrates yet another molding element 230 which can be usedin forming a medical device such as that illustrated in FIGS. 9A and 9B.This molding element comprises an outer molding section 232 defining atapered inner surface 234 and an inner molding section 236 having anouter surface 238 substantially the same shape as the tapered innersurface 234 of the outer molding section. The inner molding section 236should be sized to be received within the outer molding section, with apiece of the metal fabric (not shown) being disposed between the innerand outer molding sections. The molding surface of this molding element230, to which the fabric will generally conform, can be considered toinclude both the inner surface 234 of the outer molding section and theouter surface 238 of the inner molding section.

This molding element 230 can be used with a metal fabric which is in theform of a tubular braid. If such a fabric is used and a clamp 15 (notshown in this drawing) or the like is provided to connect the ends ofthe wire strands adjacent one end of the device, a recess (not shown)analogous to the cavity 46 in the face of the compression disk 44 ofmolding element 20 (FIGS. 2-4) can be provided for receiving the clamp.

However, the present molding element 230 can be used quite readily witha flat woven piece of metal fabric, such as is illustrated in FIG. 1B.In using such a fabric, a suitably sized and shaped piece of fabric iscut; in using the molding element 230 to produce a device 180 analogousto that shown in FIGS. 9A and 9B, for example, a generally disk-shapedpiece of the metal fabric 10′ can be used. The metal fabric is thenplaced between the two sections 232, 236 of the molding element and thesections are moved together to deform the fabric therebetween. Afterheat treatment, the fabric can be removed and will retain substantiallythe same shape as it had when it was deformed between the two moldingsections.

As can be seen by the discussion of the various molding elements 200,210 and 230 in FIGS. 10A-10C, it should be clear that a number ofdifferent molding elements may achieve essentially the same desiredshape. These molding elements may be received entirely within a closedsegment of fabric and rely on tension and/or compression of the fabricto cause it to generally conform to the molding surface of the moldingelement, as with the element 200 of FIG. 10A. The molding element 210 ofFIG. 10B substantially encloses the fabric within a recess in the moldand relies on compression of the fabric (in this case axial compressionof a tubular braid) to deform the fabric to the desired configuration.Finally, the fabric may be compressed between two coacting parts of themolding element to deform the fabric, such as between the two sections232, 236 of molding element 230 in FIG. 10C. Any one or more of thesetechniques may be used in achieving a finished product having a desiredshape.

FIGS. 11 and 12 illustrate alternative embodiments of yet anothermedical device in accordance with this invention. Both FIG. 11 and FIG.12 illustrate a vascular trap suitable for use in temporarily filteringembolic particles from blood passing through a patient's vascularsystem. Such a device will most frequently be used to filter emboli froma patient's blood when another medical procedure is being performed,such as by using the trap in conjunction with a rotating cutting bladeduring an atherectomy or with a balloon catheter during angioplasty. Itis to be understood, though, that the trap could also be used in othersimilar applications, such as in channels in patients' bodies other thantheir vascular systems.

In the embodiment of FIGS. 11A and 11B, the vascular trap 250 comprisesa generally umbrella-shaped basket 270 carried adjacent a distal end ofa guidewire 260. The guidewire in this embodiment includes a tapereddistal section 262 with a spirally wound coil 264 extending along adistal length of the wire. Guidewires having such a distal end areconventional in the art. The basket 270 is positioned generallyproximally of the coil 264, and is desirably attached to the guidewireproximally of the proximal end of the tapered section, as shown.

The basket 270 (shown in its collapsed configuration in FIG. 11A)includes a distal band 272 and a proximal band 274. The distal band maybe made of a radiopaque material, such as gold, platinum or tungsten,and is affixed directly to the shaft of the guidewire 260. Thisattachment may be made by any suitable means, such as by welding,brazing or soldering. Alternatively, the distal band 272 may comprise abead of a biocompatible cementitious material, such as a curable organicresin. If it is desired to increase the visibility of the band forfluoroscopic observation, a radiopaque metal or the like can be imbeddedin the cementitious material. The proximal band 274 may be formed of ahypotube sized to permit the tube to slide along the guidewire duringdeployment. This hypotube may be made of a metallic material; athin-walled tube of a NiTi alloy should suffice. If so desired, theproximal band may be formed of a more radiopaque metal, or a NiTi alloyband can have a radiopaque coating applied to its surface.

The body of the device is formed of a metal fabric, as explained above.The metal fabric of this embodiment is optimally initially formed as atubular braid and the ends of the wires forming the braid can beattached together by means of the bands 272, 274 before the fabric iscut to length. Much like the clamps 15, 90 noted above, these bands 272,274 will help prevent the metal fabric from unravelling during theforming process. (The method of forming the basket 270 is describedbelow in connection with FIG. 16.)

When the device is in its collapsed state for deployment in a patient'svessel (as illustrated in FIG. 11A), the basket 270 will be collapsedtoward the axis of the guidewire 260. The distal 272 and proximal 274bands are spaced away from one another along the length of theguidewire, with the fabric of the device extending therebetween. In apreferred embodiment, when the basket is in its collapsed state it willengage the outer surface of the guidewire to permit the device to bedeployed through a relatively small lumen of a catheter or anothermedical device.

When the device is deployed in a patient's vascular system, the basketwill take on an expanded configuration wherein it extends outwardly ofthe outer surface of the guidewire. As best seen in FIG. 11B, the shapeof the basket 270 when deployed may generally resemble a conventionalumbrella or parachute, having a dome-like structure curving radiallyoutwardly from the guidewire moving proximally from the distal band 272.It is to be understood that other suitable shapes could easily performthe desired filtering function, such as a conical shape wherein theslope of the device changes more linearly than the smooth, roundedversion shown in FIG. 11B. It is also believed that a relatively flat,disc shape would also suffice. In this expanded configuration, the twobands 272, 274 are closer together, with the distal band 272 optimallybeing spaced only a short distance from the proximal band 274, asillustrated.

In moving from its collapsed state (FIG. 11A) to its expanded state(FIG. 11B), the metal fabric turns in on itself, with a proximal portion282 of the collapsed basket being received within the interior of adistal portion 284 of the collapsed basket. This produces a two-layeredstructure having a proximal lip 286 spaced radially outwardly of theguidewire, defining a proximally-facing cup-shaped cavity 288 of thebasket. When blood (or any other fluid) flows through the basket in adistal direction, any particulate matter in the blood, e.g. embolireleased into the bloodstream during atherectomy or angioplastyprocedures, will tend to be trapped in the cavity 288 of the basket.

The precise dimensions of the metal fabric can be varied as desired forvarious applications. If the device 250 is to be used as a vascularfilter to trap emboli released into the blood, for example, the pores(i.e. the openings between the crossing metal strands) of the fabric aredesirably on the order of about 1.0 mm. This is generally deemed to bethe minimum size of any particles which are likely to cause any adverseside effects if they are allowed to float freely within a blood vessel.One would not want to make the pores too small, though, because theblood (or other fluid) should be free to pass through the wall of thebasket 270. If so desired, the basket may be coated with a suitableanti-thrombogenic coating to prevent the basket from occluding a bloodvessel in which it is deployed.

When a fabric having 1.0 mm pores is used to form the basket 270 of thisembodiment of the invention, the forming process will reorient the wiresrelative to one another and in some areas (e.g. adjacent the proximallip 286) the pores will be larger than 1.0 mm. However, because thebasket's walls are formed of essentially two thicknesses 282, 284 of thefabric, the effective pore size of the device may be significantlyreduced even at these locations.

The device 250 may also be provided with tethers 290 for collapsing thebasket 270 during retraction. The basket may include four independenttether wires, each of which extends proximally from the proximal lip 286of the deployed basket. In a preferred embodiment, though, the fourtether wires illustrated in the drawings are actually formed of twolonger wires, with each wire extending peripherally about a portion ofthe proximal lip of the basket. These tether wires may be intertwinedwith the wires of the metal fabric to keep the tethers in place duringuse. When the tethers are retracted or drawn down toward the guidewire,the wires extending along the proximal lip of the basket will tend toact as drawstrings, drawing the proximal end of the basket radiallyinwardly toward the guidewire. This will tend to close the basket andentrap any material caught in the cavity 288 of the basket during use sothat the basket can be retracted, as detailed below.

The tether wires 290 may extend along much of the length of theguidewire so that they will extend outside the patient's body during useof the device 250. When it is desired to collapse the basket forretrieval, the operator can simply hold the guidewire 260 steady andretract the tethers with respect to the guidewire. This can tend to berelatively cumbersome, though, and may be too difficult to effectivelyaccomplish without breaking the tethers if the device is deployed at aselective site reached by a tortuous path, such as in the brain.

Accordingly, in the preferred embodiment shown in FIGS. 11A and 11B, thetethers 290 are attached to the guidewire 260 at a position spacedproximally of the basket. The tethers may, for example, be attached to ametal strap 292 or the like and this strap 292 may be affixed to theshaft of the guidewire. When it is desired to close the proximal end ofthe basket for retraction, an external catheter (not shown) can be urgeddistally toward the basket 270. When the catheter encounters theradially extending tethers, the distal end of the catheter will tend todraw the tethers toward the guidewire as the catheter is advanced, whichwill, in turn, tend to draw the proximal end of the basket closed.

FIGS. 12A and 12B illustrate an alternative embodiment of the deviceshown in FIGS. 11A and 11B, with FIG. 12A showing the device collapsedin a catheter C for deployment and FIG. 12B showing the device in itsdeployed configuration. In the embodiment shown in FIGS. 12A and 12B,the basket 270 is formed substantially the same as outlined above inconnection with FIGS. 11A and 11B. In the embodiment of FIGS. 12,though, the distal band 272 is affixed to the guidewire 260′ at thedistal tip of the guidewire. The guidewire 260′ is of the type referredto in the art as a “movable core” guidewire. In such guidewires, a corewire 265 is received within the lumen of a helically wound wire coil 266and the core wire 265 extends distally beyond the distal end of the coil266. A thin, elongate safety wire 268 may extend along the entire lumenof the coil 266 and the distal end of the safety wire may be attached tothe distal end of the coil to prevent loss of a segment of the coil ifthe coil should break.

In the embodiment of FIGS. 11, the proximal ends of the tethers 290 areattached to a metal strap 292 which is itself attached to the shaft ofthe guidewire 260. In the present embodiment, the tethers are notattached to the core wire 265 itself. Instead, the tethers are attachedto the coil 266 of the guidewire. The tethers may be attached to thecoil by any suitable means, such as by means of laser spot welding,soldering or brazing. The tethers 290 may be attached to the coil 266 atvirtually any spot along the length of the coil. As illustrated in thesedrawings, for example, the tethers may be attached to the coil adjacentthe coil's distal end. However, if so desired the tethers may beattached to the coil at a location spaced more proximally from thebasket 270.

An external catheter such as that referred to in the discussion of FIGS.11A, but not shown in those drawings, is illustrated in FIGS. 12A and12B. Once the basket 270 is deployed in a patient's vessel tosubstantially reach the expanded configuration shown in FIG. 12B and thebasket has performed its intended filtration function, the externalcatheter C can be urged distally toward the basket 270. As this catheteris urged forward, the tethers will tend to be drawn into the distal endof the catheter, which is substantially narrower than the proximal lip286 of the basket. This will tend to draw the tethers down toward theguidewire and help close the basket, as explained above.

FIGS. 13-15 illustrate yet another alternative embodiment of a vasculartrap in accordance with the present invention. This vascular trap 300includes a basket 320 received over a guidewire 310. In most respects,the basket 320 is directly analogous to the basket 270 illustrated inFIGS. 11-12. The basket 320 includes a proximal band 324 and a distalband 322. As in the embodiment of FIGS. 12A and 12B, the distal band maybe attached to the guidewire adjacent its distal end. If so desired,though, a structure such as is shown in FIGS. 11, wherein the guidewireextends distally beyond the basket, could instead be used.

As best seen in its collapsed state (shown in FIG. 13), the basketincludes a distal segment 325 and a proximal segment 326, with thedistal end of the distal segment being attached to the distal band 322and the proximal end of the proximal segment being attached to theproximal band 324. When the basket 320 is in the expanded configuration(shown in FIG. 14), the proximal segment 326 is received within thedistal segment 325, defining a proximal lip 328 at the proximal edge ofthe device. The wall of the basket thus formed also includes a cavity329 for trapping solids entrained in a fluid, such as emboli in apatient's blood stream.

The basket 320 of FIGS. 13-15 is also shaped a little bit differentlythan the basket 270 of the previous drawings. The primary differencebetween these two baskets is that the basket 320 is a little bit shorteralong its axis than is the basket 270. This different basket shape issimply intended to illustrate that the basket of a vascular trap inaccordance with the invention can have any of a wide variety of shapesand no particular significance should be attached to the slightlydifferent shapes shown in the various drawings.

In the vascular traps 250 and 250′ of FIGS. 11 and 12, respectively,tethers were used to draw down the proximal end of the basket 270 toclose the basket for retraction. In the embodiment shown in FIGS. 13-15,though, the trap 300 includes a basket cover 340 positioned proximallyof the basket 320. The basket cover may also be formed of a metallictubular braid and is also adapted to be collapsed to lay generally alongthe outer surface of the guidewire 310. The cover 340 is not directlyaffixed to the guidewire at any point, though, but is instead intendedto be slidable along the guidewire. As best seen in FIGS. 13 and 14wherein the cover is in its collapsed state, the cover 340 includes adistal hypotube 342 and a proximal control hypotube 344, with the distalhypotube being attached to the distal end of the cover 340 and theproximal control hypotube 344 being attached to the proximal end of thecover.

The cover 340 is shown in its deployed, expanded configuration in FIG.15. As shown in that figure, the cover has a similar structure to thatof the basket 320, but is oriented to be open distally rather thanproximally, as is the basket. As best seen in FIGS. 13 and 14 whereinthe cover is in its collapsed state, the cover has a distal segment 352and a proximal segment 354. When the cover is deployed by urging itdistally out of the distal end of the deployment catheter C, the cover340 will tend to resiliently return to its expanded configuration andthe distal hypotube 342 will slide axially proximally along theguidewire toward the proximal control hypotube 344. This will invert thecollapsed cover so that the distal section 352 is generally receivedwithin the proximal section 354, defining a distal lip 358 of the cover.

The proximal control hypotube 344 may extend along a substantial portionof the length of the catheter 310 so that it extends out of thepatient's body when the device 300 is in place. By grasping the controlhypotube and moving it relative to the guidewire 310, an operator cancontrol the position of the cover 340 with respect to the basket 320,which is affixed to the guidewires. As explained in more detail below inconnection with the use of the device 300, once the basket has beendeployed and has been used to filter objects entrained in the fluid(e.g. emboli in blood), the cover 340 may be deployed and the trap maybe drawn proximally toward the cover by moving the guidewire proximallywith respect to the control hypotube 344.

The inner diameter of the distal lip 358 of the cover is desirablyslightly larger than the outer diameter of the proximal lip 328 of thebasket. Hence, when the basket is drawn proximally toward the cover itwill be substantially enclosed therein. The cover will therefore tend totrap any emboli (not shown) or other particulate matter retained withinthe cavity 330 of the basket. A retrieval sheath S may then be urgeddistally to engage the outer surface of the cover 340. This will tend tocause the cover to collapse about the basket, tightly engaging the outersurface of the basket. This somewhat collapsed structure can then bewithdrawn from the patient's channel and removed from the patient'sbody. By enclosing the basket within the cover, the likelihood of anyfiltered debris within the basket being lost as the basket is retrievedwill be substantially eliminated.

The guidewire and the metal fabric can be of any diameter suitable forthe intended application of the vascular trap 250, 250′ or 300. In apreferred embodiment, the guidewire is between about 0.014″ and about0.038″ in diameter and the wires of the metal fabric used to form thebasket (and the cover 340, if a cover is included) are between about0.002″ and about 0.006″. The thickness of the metal bands (272, 274 or322, 324) also is desirably in the range of about 0.002″-0.006″.

In one particularly preferred embodiment intended to be used in narrowervessels such as those encountered in cerebral and coronary applications,the guidewire has an outer diameter of about 0.014″ and the wires of themetal fabric are about 0.002″ in diameter. The metal bands in thisembodiment may also have a thickness of about 0.002″ so that they willnot be substantially wider than the collapsed basket. When the device iscollapsed for deployment through a catheter, it will have an outerdiameter of about 0.018″, permitting the device to be used withcatheters and other instruments adapted for use with a 0.018″ guidewire.

FIG. 16 illustrates one embodiment of a molding element 370 which may beused in making a basket 270. Although the basket 320 and cover 340 ofthe trap 300 are shaped somewhat differently, an analogous moldingelement can be used for these portions of the trap 300 as well by simplymodifying some of the dimensions of the molding element 370, butretaining the basic shape and structure of the molding element. It alsoshould be understood that the molding element 370 is merely one possiblemolding element for forming a shape such as that of the basket 270 andthat any one of a variety of different molding elements will be apparentto those skilled in the art, as noted above in connection with FIGS.10A-C.

The molding element 370 has an outer molding section 372 defining acurved inner surface 374 and an inner molding section 376 having anouter surface 378 substantially the same shape as the curved innersurface 374 of the outer molding section. The inner molding section 376should be sized to be received within the outer molding section, with apiece of the metal fabric (not shown) being disposed between the innerand outer molding sections. In a preferred embodiment, the inner surface374 of the outer molding element and the outer surface 378 of the innermolding section each include a recess (375 and 379, respectively) forreceiving an end of the braid. The molding surface of this moldingelement 370, to which the fabric will generally conform, can beconsidered to include both the inner surface 374 of the outer moldingsection and the outer surface 378 of the inner molding section.

In use, the two molding sections 372, 376 are spaced apart from oneanother and a length of a tubular braid of metal fabric (not shown inFIG. 16) is disposed between these molding sections. Optimally, one endof the fabric is placed in the recess 375 of the outer molding sectionand the other end of the fabric is placed in the recess 379 in the innermolding section. The inner and outer molding sections can then be urgedgenerally toward one another. As the ends of the wire approach oneanother, the tubular braid will tend to invert upon itself and a surfaceof the tubular braid will generally conform to either the inner surface374 of the outer molding section or the outer surface 378 of the innermolding section, arriving at a shape analogous to that of the basket 270of the traps 250, 250′. The two molding sections can then be locked inplace with respect to one another and the metal fabric may be heattreated to set the wires in this deformed configuration.

The method in accordance with the present invention further includes amethod of treating a physiological condition of a patient. In accordancewith this method, a medical device suitable for treating the condition,which may be substantially in accordance with one of the embodimentsoutlined above, is selected. For example, if a patent ductus arteriosusis to be treated, the PDA occlusion device 80 of FIGS. 6A-6C can beselected. Once the appropriate medical device is selected, a cathetermay be positioned within a channel in a patient's body to place thedistal end of the catheter adjacent the desired treatment site, such asimmediately adjacent (or even within) the shunt of the PDA.

Medical devices made in accordance with the method of the inventionoutlined above have a preset expanded configuration and a collapsedconfiguration which allows the device to be passed through a catheter.The expanded configuration is generally defined by the shape of themedical fabric when it is deformed to generally conform to the moldingsurface of the molding element. Heat treating the metal fabricsubstantially sets the shapes of the wire strands in the reorientedrelative positions when the fabric conforms to the molding surface. Whenthe metal fabric is then removed from the molding element, the fabricmay define a medical device in its preset expanded configuration.

The medical device can be collapsed into its collapsed configuration andinserted into the lumen of the catheter. The collapsed configuration ofthe device may be of any shape suitable for easy passage through thelumen of a catheter and proper deployment out the distal end of thecatheter. For example, the devices shown in FIGS. 5 may have arelatively elongated collapsed configuration wherein the devices arestretched along their axes. This collapsed configuration can be achievedsimply by stretching the device generally along its axis, e.g. bymanually grasping the clamps 15 and pulling them apart, which will tendto collapse the expanded diameter portions 64 of the device 60 inwardlytoward the device's axis. The PDA occlusion device 80 of FIGS. 6 alsooperates in much the same fashion and can be collapsed into itscollapsed configuration for insertion into the catheter by applyingtension generally along the axis of the device. In this regard, thesedevices 60 and 80 are not unlike “Chinese handcuffs”, which tend toconstrict in diameter under axial tension.

Once the medical device is collapsed and inserted into the catheter, itmay be urged along the lumen of the catheter toward the distal end ofthe catheter. This may be accomplished by using a guidewire or the liketo abut against the device and urge it along the catheter. When thedevice begins to exit the distal end of the catheter, which ispositioned adjacent the desired treatment site, it will tend toresiliently return substantially entirely to its preset expandedconfiguration. Superelastic alloys, such as nitinol, are particularlyuseful in this application because of their ability to readily return toa particular configuration after being elastically deformed to a greatextent. Hence, simply urging the medical device out of the distal end ofthe catheter tends to properly deploy the device at the treatment site.

Although the device will tend to resiliently return to its initialexpanded configuration (i.e. its shape prior to being collapsed forpassage through the catheter), it should be understood that it may notalways return entirely to that shape. For example, the device 60 of FIG.5 is intended to have a maximum outer diameter in its expandedconfiguration at least as large as and preferably larger than, the innerdiameter of the lumen in which it is to be deployed. If such a device isdeployed in a vessel having a small lumen, the lumen will prevent thedevice from completely returning to its expanded configuration.Nonetheless, the device would be properly deployed because it wouldengage the inner wall of the lumen to seat the device therein, asdetailed above.

If the device is to be used to permanently occlude a channel in thepatient's body, such as the devices 60 and 80 described above may be,one can simply retract the catheter and remove it from the patient'sbody. This will leave the medical device deployed in the patient'svascular system so that it may occlude the blood vessel or other channelin the patient's body. In some circumstances, the medical device may beattached to a delivery system in such a manner as to secure the deviceto the end of the delivery means, such as when the threaded clamp 90shown in FIGS. 6 and 9 is attached to a distal end of the deliverymeans, as explained above. Before removing the catheter in such asystem, it may be necessary to detach the medical device from thedelivery means before removing the catheter and the delivery means.

The devices of FIGS. 11-15 may be deployed in much the same fashionoutlined above. However, these devices 250, 250′ and 300 areadvantageously deployed for use in conjunction with another medicaldevice and will most frequently be retracted from the patient's bodyafter use.

For example, any one of these devices are suitable for use inconjunction with a balloon angioplasty procedure. In such procedures,catheters having inflatable balloons at their ends, referred to asballoon catheters, are positioned within a blood vessel so that theballoon is positioned within a stenosis. These balloons are positionedby tracking the balloon catheter along a guidewire or the like; theballoons typically have a central bore therethrough. Once the balloon isproperly positioned, it is inflated and urges radially outwardly againstthe stenosis. This will tend to squeeze the stenosis against the wallsof the vessel, improving patency of the vessel.

When the stenosis is treated in this fashion, though, there is a riskthat some debris will break free and enter the blood flowing through thevessel. If left unchecked, this embolus can drift downstream andembolize a distal portion of the vessel. Depending on where the emboluscomes to rest, the embolization can result in significant tissue ororgan damage. This risk is particularly acute in cardiac and coronaryapplications because the embolization can result in a myocardialinfarction or heart attack, and in neurovascular and interventionalradiological procedures the embolization can lead to a stroke or damageto brain tissue.

In order to prevent, or at least substantially limit, such embolization,a vascular trap 250, 250′ or 300 of the invention can be used with theballoon catheter. The device should be sized to permit it to be passedthrough the lumen of the particular balloon catheter to be used in theangioplasty.

In one embodiment of a method for using such a vascular trap, the trapis deployed first. The basket (270 or 320) of the trap will be guided toa position located downstream of the desired treatment site through anintroduction catheter (e.g. the catheter C in FIGS. 12-15). The basketis then urged distally beyond the end of the catheter, which will permitthe basket to resiliently substantially return to its expandedconfiguration from its collapsed configuration within the catheter. Oncethe trap is in place, the balloon catheter can be exchanged for theintroduction catheter, and the balloon catheter can track the guidewire(260 or 310) of the vascular trap. The balloon can then be positionedwithin the stenosis and expanded, as outlined above. Once theangioplasty has been completed, the balloon can be deflated again andwithdrawn proximally out of the patient.

In an alternative embodiment of the present method, the balloon cathetercan be used to perform the same function as performed by theintroduction catheter in the preceding embodiment. In this embodiment,the balloon catheter is positioned in the patient's vessel so that thedistal end of the balloon catheter is located downstream of thestenosis. The vascular trap (250, 250′ or 300) of the invention is thenpassed through the lumen of the balloon catheter and the basket is urgedout of the distal end of the catheter. The basket will resilientlysubstantially return to its preferred expanded configuration, whereuponthe balloon catheter can be retracted along the shaft of the device'sguidewire until the balloon is properly positioned within the stenosis.

If so desired, the balloon catheter can instead be provided with alength of standard catheter extending distally beyond the distal end ofthe balloon. The balloon can then be positioned within the stenosis andthe basket can be urged out of the distal end of the distal extension ofthe catheter. In such an embodiment, the length of the distal extensionof the catheter should be sufficient to properly position the basketwith respect to the balloon when the basket exits the distal end of thecatheter. This will eliminate the need to perform the separate step ofretracting the balloon into position within the stenosis after thebasket is deployed. The balloon can then be expanded, deflated andwithdrawn as described above.

Much the same procedure can be used to deploy a vascular trap of theinvention for use in an atherectomy procedure. In such procedures, acutting head is positioned at the distal end of an elongate, hollowshaft and the cutting head has a bore extending therethrough. The trapcan be deployed in either of the methods outlined above, but it isanticipated that in most instances the first procedure will be used,i.e. the basket will be deployed with an introduction catheter, whichwill be removed so that the cutting device can be guided over theguidewire of the vascular trap. It should also be understood that thedevice 250, 250′ and 300 could also be used in other medical proceduresin other 5 bodily channels besides a patient's vascular system.

Since the trap is positioned downstream of the stenosis, any debrisreleased during the procedure will tend to drift distally toward thebasket and be caught therein. In order to prevent any emboli from simplyfloating past the trap, it is preferred that the proximal lip (288 or328) of the basket be at least as large as the lumen of the vessel. In apreferred embodiment, the natural dimension of the proximal lip (i.e.where the basket has fully returned to its expanded configuration) issomewhat greater than the vessel's inner diameter so that the basketwill firmly engage the wall of the vessel.

The method of retracting the basket will depend on which embodiment ofthe vascular trap is used, namely whether or not the device includes acover 340. The devices 250 or 250′ of FIGS. 11 or 12, respectively, donot include such a cover. However, they do include tethers 290 whichextend proximally from the proximal lip 288 of the basket to anattachment to the guidewire. In either of these embodiments, a retrievalcatheter can be introduced over the guidewire and urged distally towardthe basket. As explained above in connection with FIGS. 11 and 12, thiswill tend to draw the tethers down toward the guidewire, effectivelyclosing the proximal end of the basket 270. Once the basket issufficiently closed, such as when the proximal lip of the basket engagesthe distal tip of the retrieval catheter, the catheter and the vasculartrap can be retracted together from the patient's body. By substantiallyclosing the proximal end of the basket in such a fashion, any emboliwhich are captured in the basket when it is deployed can be retainedwithin the basket until it is removed from the patient's body.

If so desired, a balloon catheter or like device can instead be used,with the balloon catheter being used to draw down the tethers 290 andcollapse the basket. The vascular trap can then be withdrawn with theballoon catheter rather than having to separately introduce a removalcatheter to remove the trap.

In withdrawing the embodiment illustrated in FIGS. 13-15, the cover 340is positioned over the proximal lip of the basket before the vasculartrap 300 is retracted. Once the medical procedure is completed and anydebris has been captured in the basket, the cover 340 is allowed toresiliently substantially return to its expanded configuration. Once itis deployed proximally of the basket, the basket 320 can be drawnproximally toward the cover 340 until it engages or is received withinthe cover, as noted above in connection with FIG. 15.

In actuality, the cover 340 may be unable to return to its full expandedconfiguration due to the confines of the vessel in which it is deployed.As explained previously, the cover 340 is desirably larger than thebasket 320 so that the basket can be received within the cover. However,the basket is optimally sized to engage the walls of the vessel toprevent the unwanted passage of emboli or other debris around the edgesof the basket. Accordingly, the distal lip 358 of the cover will engagethe wall of the channel before it expands to its full size. The walls ofmost bodily channels, such as blood vessels, tend to be somewhatelastic, though. The cover 340 will therefore tend to urge harderagainst the wall of the vessel than the smaller basket and may stretchthe vessel a little bit more than will the basket. In this fashion, thecover may still be able to expand to a dimension large enough to permitthe basket to be received in the cavity 356 of the cover. If not, thedistal lip 358 of the cover can simply be brought into close engagementwith the proximal lip 328 of the basket to generally seal the basket.

Once the cover 340 is brought into engagement with the basket 320,whether by receiving the basket within the cover or, less preferably, byengaging the lips 358, 328 of the cover and the basket, the device canbe withdrawn proximally from the patient's vascular system. The coverwill tend to prevent any emboli caught in the basket during deploymentfrom being inadvertently lost during withdrawal.

The vascular traps 250, 250′ and 300 of the present invention thereforehave distinct advantages over other vascular traps or filters currentlyknown in the art. As explained above, most prior art traps are difficultand expensive to form and cannot be readily collapsed for retrieval. Thepresent invention, though, provides a method for making the vasculartraps 250, 250′ and 300 which is both relatively inexpensive and lesslabor intensive, generally resulting in a more consistent product thanprior art hand-forming methods. Furthermore, the structure of the deviceand the methods outlined above for removing the device will fairlyreliably prevent the inadvertent dumping of trapped emboli back into thebloodstream while the device is being removed. Since most prior arttraps and filters are much more difficult to use and are more likely todump filtered debris back into the bloodstream, the present inventioncan be substantially safer than these prior art systems.

While a preferred embodiment of the present invention has beendescribed, it should be understood that various changes, adaptations andmodifications may be made therein without departing from the spirit ofthe invention and the scope of the appended claims.

1. A method for filtering emboli from blood flowing through a bodyvessel comprising: providing a guidewire having distal and proximal endsand carrying a filter non-removable from the guidewire on a distalportion of the guidewire, the filter being expandable from a collapseddelivery configuration to an expanded deployed configuration; providingan introduction catheter having distal and proximal ends and a lumensized to receive the guidewire; providing a retrieval catheter havingdistal and proximal ends and a lumen sized to receive the guidewire;introducing the introduction catheter into the vessel; advancing theguidewire through the vessel while the filter is contained within thelumen of the introduction catheter in its collapsed deliveryconfiguration; expanding the filter to its expanded deployedconfiguration at a location within the vessel distal to the treatmentsite; removing the introduction catheter from the vessel; filteringemboli from blood with the filter; after the introduction catheter hasbeen removed introducing the distal end of the retrieval catheter intothe vessel; advancing the retrieval catheter over the guidewire toretrieve the filter; and removing the retrieval catheter, guidewire andfilter from the vessel.
 2. The method of claim 1 wherein at least aportion of the filter is self-expanding.